The present invention is directed to a method for synthesizing polymeric azo dyes from a diazonium salt and a polymer. The resulting polymeric azo dye compounds are useful in antireflective coating compositions used in conjunction with photoresist materials in producing microelectronic devices.
It has been observed that many chemical manufacturing processes, which provide acceptable results on a small or lab scale, prove to be impractical or not economical, when an attempt is made to adopt such processes to large-scale production. This is true when preparing products via fast reaction(s) of two or more compounds, which are contained in two or more separate phases. This type of fast reaction requires rapid interfacial mixing (in both the macro and micro scope) so that the reactant carried in one phase makes immediate intimate contact with the reactant(s) contained in the other phase(s). This enables an efficient and substantially complete chemical reaction(s) to take place between the reactants from all phases before possible competitive side reactions take place. An example of such a reaction is the azo-coupling of a polymer with a diazonium salt. When the diazonium salt is reacted with the polymer under basic conditions the result is the addition of an azo chromophore to the polymer, for example as set forth below: 
The diazonium salt may be soluble in one solvent, such as water, producing a first phase. The polymer may be soluble in another solvent, such as an organic solvent, which produces a second separate phase. Such an azo coupling is capable of taking place in a very short period of time, provided that there is intimate mixing and sufficient contact between the reactants.
For the purposes of this application, a diazonium salt is preferably derived from the diazotization of a corresponding amine, preferably an aromatic amine, followed by a diazotizing reagent, such as a nitrite salt, in the presence of an acid, such as HCl, H2SO4, etc. Most diazonium salts are relatively stable in acidic conditions at a cold temperature, from about 0xc2x0 C. to about 15xc2x0 C. However, if the polymer solvent blend with which the diazonium salt is reacted is basic, this can have an adverse impact because the diazonium salt tends to decompose or undergo side reactions, under such basic conditions, to form a number of possible undesirable side products, for example as set forth below: 
Therefore, if the coupling reaction proceeds too slowly, the diazonium salt has sufficient time to undergo such side reactions or decomposition and the desired end product is not obtained.
When a chromophore, such as a diazonium salt is added to a polymer the standard practice would be to use a reaction vessel equipped with an agitator. In the lab when small vessels are employed, this set up works well at high agitation speeds. As the size of the vessel increases this set up loses its effectiveness, resulting in progressively lower yields of the desired product. In experimental settings with one-kilogram or smaller scale equipment, some options may still be available to improve the overall mixing in the vessel, such as the addition of more than one agitator or additional agitation blades. However, in scaling up for large-scale commercial production, these options may be too costly. Running the reaction on a commercial scale without sufficient agitation results in a very poor yield of the desired product and the generation of undesired side products that are difficult and costly to remove. Therefore, a need exists for a commercial-scale chemical process, which favors the azo coupling of the polymer while at the same time substantially reducing the competing reaction(s), such as the decomposition of the diazonium salt.
U.S. Pat. No. 5,886,102 teaches that in the production of antireflective coating compositions the xe2x80x9cgrafting of chromophore units onto a preformed resin often provides a resin mixture of polymers with varying percentages of chromophore. Such differing quantities of chromophore units can compromise resolution of an image patterned into an overcoated photoresist layer as the chromophore differences may result in essentially random reflections of exposure radiation.xe2x80x9d This reference goes on to explain that xe2x80x9c[g]rafting chromophore units onto at least some types of preformed polymers may be quite difficult, or simply not possible, particularly in larger scale productions. For example, it can be particularly difficult to drive the reaction to completion resulting in undesired products which must be removed from desired materials.xe2x80x9d
An article in Chemical Engineering and Processing teaches the synthesis of an azo dye via azo coupling of a diazonium salt and a monomer. Specifically, the monomer, 1-naphthol, is reacted with a diazotized sulphanilic acid solution using a static in-line mixer. The static mixer is described as having no moving parts, instead it consists of fixed elements that progressively reduce radial gradients of concentration and temperature by combining, stretching, splitting and recombining two separate but miscible streams.
It should be noted that phase transfer catalysts are available for the reaction of two or more reactants contained in two or more separate phases. Such catalysts can be used in cases where the purity of the final product is not a major concern. However, in applications where even relatively low levels of impurities pose a problem, a phase transfer catalyst is not an option because it may be too costly and very difficult, if not impossible, to separate such impurities from the desired final product. This is especially true in applications where impurities are required to be from less than 1 part per million to as low as less than 20 parts per billion.
A method for coupling a diazonium salt with a polymer is provided, which method comprises, in the following order, the steps of: dissolving an organic polymer having a weight average molecular weight ranging from about 500 to 2,000,000 in a solvent, and thereby providing one liquid phase; providing a diazonium salt in another solvent, and thereby providing a separate liquid phase; contacting the diazonium salt with the organic polymer, preferably by intimately mixing the separate phases, for a time at least equal to the minimum reaction time required to react the diazonium salt with the polymer (xe2x80x9cminimum contact timexe2x80x9d), and thereby reacting the diazonium salt and the organic polymer for a period of time at least equal to such minimum reaction time. Preferably the mole ratio of organic polymer to diazonium salt is from 90:10 to 10:90, more preferably from about 75:25 to 25:75, and most preferably from 60:40 to 40:60.
An in-line mixing unit capable of intimate mixing is preferably provided, which (mixing unit) has a sufficient length to provide a contact time that is greater than or equal to the minimum reaction time. The in-line mixing unit is preferably selected from a static tubular reactor or a dynamic mixer. The organic polymer and diazonium salt are preferably reacted in the in-line mixing unit, which initially provides rapid interphase macro- and micro-mixing, thus enabling an efficient and substantially complete chemical reaction to take place, without any substantial side reactions or decomposition of the diazonium salt.
A process for producing an antireflective coating composition is also provided, which process comprises, in the following order, the steps of: dissolving an organic polymer having a weight average molecular weight ranging from about 500 to 2,000,000 in a solvent, and thereby providing one liquid phase; providing a diazonium salt in another solvent and thereby providing a separate liquid phase; contacting the diazonium salt in contact with the organic polymer, preferably by intimately mixing the separate phases, for a time at least equal to the minimum reaction time required to react the diazonium salt with the polymer (xe2x80x9cminimum contact timexe2x80x9d), and thereby reacting the diazonium salt and the organic polymer for a period of time at least equal to such minimum reaction time. The organic polymer-diazonium salt reaction product is then dissolved in a suitable solvent, thereby providing an antireflective coating composition.
A process is also provided for forming an image on a substrate, which process comprises, in the following order: dissolving an organic polymer, having a weight average molecular weight ranging from about 500 to 2,000,000 in a solvent, and thereby providing one liquid phase; providing a diazonium salt in another solvent, and thereby providing a separate liquid phase; contacting the diazonium salt with the organic polymer, preferably by intimately mixing the separate phases, for a time at least equal to the minimum reaction time required to react the diazonium salt with the organic polymer (xe2x80x9cminimum contact timexe2x80x9d), and thereby reacting the diazonium salt and the organic polymer for a period of time at least equal to such minimum reaction time. The organic polymer-diazonium salt reaction product is then dissolved in a solvent, thereby providing an antireflective coating composition. The process further comprises, in the following order; either before or after coating a photoresist composition onto a suitable substrate, coating the antireflective coating composition onto such a suitable substrate; heating the coated substrate, and thereby substantially removing the photoresist solvent; imagewise exposing the photoresist composition; and developing the imagewise exposed photoresist composition.